Add comments to GetFullMetadataNameForFileName

Author: Sergio0694

CommunityToolkit.Mvvm.SourceGenerators/Extensions/INamedTypeSymbolExtensions.cs

@@ -33,6 +33,10 @@ static StringBuilder BuildFrom(ISymbol? symbol, StringBuilder builder)
             };
         }
 
+        // Build the full metadata name by concatenating the metadata names of all symbols from the input
+        // one to the outermost namespace, if any. Additionally, the ` and + symbols need to be replaced
+        // to avoid errors when generating code. This is a known issue with source generators not accepting
+        // those characters at the moment, see: https://github.com/dotnet/roslyn/issues/58476.
         return BuildFrom(symbol, new StringBuilder(256)).ToString().Replace('`', '-').Replace('+', '.');
     }